Method and system for handling of special SCell selection in dual connectivity

ABSTRACT

Method and system for handling of special SCell selection in dual connectivity. The present invention relates to the field of wireless communication networks and more particularly to a User Equipment (UE) operating in dual connectivity mode in wireless communication networks. The principal object of the embodiments herein is to provide a method and system for handling of special SCell (PSCell) change by extending Event A3 or Event A5 to PSCell for relative comparison. Another object of the invention is to provide a method and system for handling of special SCell (PSCell) change with a new Event Ax.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 16/198,323, filed on Nov. 21, 2018, which is a continuationapplication of prior application Ser. No. 15/112,379, filed on Jul. 18,2016, which issued as U.S. patent Ser. No. 10/194,425, which is a U.S.National Stage application under 35 U.S.C. § 371 of an Internationalapplication number PCT/KR2015/000524, filed on Jan. 19, 2015, which isbased on and claimed priority of an Indian patent application number202/CHE/2014, filed on Jan. 17, 2014, in the Indian IntellectualProperty Office and of an Indian patent application number1606/CHE/2014, filed on Mar. 26, 2014 in the Indian IntellectualProperty Office, the disclosure of each of which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present invention relates to the field of wireless communicationnetworks and more particularly to a User Equipment (UE) operating indual connectivity mode in wireless communication networks.

BACKGROUND ART

With rise in deployment of Long Term Evolution (LTE) and LTE advanced(LTE-A), small cells using low power nodes such as Pico cells and Femtocells are considered promising to cope with mobile traffic explosion. Asmall cell using a low power node, which has transmission power (Tx)lower than a macro node and Base Station (BS) classes is preferred forhotspot deployments in indoor and outdoor scenarios resulting inenhanced performance.

The small cell enhancement for Evolved Universal MobileTelecommunication System (UMTS) Terrestrial Radio Access Network(E-UTRAN) and E-UTRA focuses on additional functionalities for enhancedperformance in hotspot areas for indoor and outdoor using the low powernodes.

3GPP (3^(rd) Generation Partnership Project) is considering use ofpotential higher layer technologies for enhanced support of small celldeployments in E-UTRA (Evolved UMTS (Universal Mobile TelecommunicationsSystem) Terrestrial Radio Access) and E-UTRAN (Evolved UMTS TerrestrialRadio Access Network) to fulfill the deployment scenarios and therequirements specified in TR 36.932.

3GPP is considering a deployment scenario, in which different frequencybands are separately assigned to macro layer and small cell layer,respectively. Small cell enhancement is expected to supportsignificantly increased user throughput for both downlink and uplinkwith main focus on typical user throughput considering a reasonablesystem complexity. Small cell enhancement is expected to target thecapacity per unit area (e.g. bps/km2) to be as high as possible, for agiven user and small cell distribution, typical traffic types andconsidering a reasonable system complexity. The small cell enhancementsare also expected to consider the impact of the actual backhaul delaysand provide solutions with the aim of improved system performance. Otheraspects, for example service quality of VoLTE (Voice over LTE (Long TermEvolution)) (e.g. MOS (Mean Opinion Score)) and delay/jitter impacts onservices (video streaming, video calls and so on), could also beaddressed later.

In LTE Release-10 carrier aggregation, all the component carriersinvolved in carrier aggregation is handled at the same eNB (co-located)and the component carriers are from the same frequency band i.e.intra-band carrier aggregation. In LTE Release-11 specification supportsinter-band carrier aggregation where the component carriers are fromdifferent frequency bands. In the inter-band carrier aggregationscenario, the component carrier (F1) from a lower frequency band canprovide coverage and mobility whereas the other component carrier (F2)from a higher frequency band can provide high throughput to the UE. Theinter-band carrier aggregation could be non-co-located, where the UE iscarrier aggregated with at least one first serving frequency by a MastereNodeB (MeNB) and at least one second serving frequency served by aSecondary eNB (SeNB). When carrier aggregation between at least one cellcontrolled by two geographically separated eNBs is envisioned then it iscalled as inter-eNB carrier aggregation and the UE is said to beconfigured with dual connectivity mode of operation. In such a scenario,dual connectivity is envisioned such that the UE maintains physicallinks with at least one cell controlled by two geographically separatedeNBs. The UE maintains dual connectivity both in downlink and uplink oronly downlink. In uplink the dual connectivity towards the MeNB and theSeNB could be simultaneous or could be time multiplexed.

In the so-called dual connectivity mode of operation, the UE consumesradio resources provided by two different network nodes (i.e. MeNBassociated with at least one first serving frequency and SeNB associatedwith at least one second serving frequency) connected via a non-idealbackhaul interface (X2 interface). The MeNB also called first eNB isresponsible for managing the resources i.e. carriers or cells belongingto MeNB referred as Master Cell Group (MCG). The MeNB is the eNB whichhosts the Radio Resource Control (RRC) layer and a single S1-MMEtermination point exists for an UE configured with dual connectivitymode of operation between the Mobile Management Entity (MME) and theE-UTRAN. The MeNB therefore acts as a mobility anchor towards the corenetwork (CN). The SeNB (also called second eNB) is an eNB providingadditional radio resources for the UE. The SeNB is responsible formanaging the resources i.e. carriers or cells belonging to SeNB referredas Secondary Cell Group (SCG). The eNB configured as SeNB for a given UEcould also be operated as a normal LTE cell for standalone UEs. TheE-UTRAN architecture and related functions to support Dual Connectivityfor E-UTRAN is further described in TS 36.300.

The standard procedure for the intra-frequency and inter-frequency LTE(i.e. handover between LTE cells) handover in LTE specification (i.e.3GPP TS 36.331) is described herein.

An event A1 is triggered when the signal strength of the serving cell(wherein the UE is connected to the serving cell), which is measured bythe UE, greater than a threshold value.

An event A2 is triggered when the signal strength of the serving cell,which is measured by the UE, is less than a threshold value, wherein theUE is connected to the serving cell, but the signal strength of theserving cell is not strong enough.

An event A3 is triggered when the signal strength of a neighboring cell(managed by the same or a different eNB) is greater than that of theserving cell and the difference between the signal strengths of theserving cell and the neighbor cell is greater than a predefined offset.If the event A3 is detected, the UE predicts that a handover will occurin the near future. Event A3 is applicable for both intra-frequency andinter-frequency LTE cells for relative comparison.

An event A4 is triggered when the signal strength of the neighboringcell (managed by same or a different eNB), which is measured by the UE,is greater than a threshold value.

An event A5 is triggered when the signal strength of the serving cell isless than a predefined first threshold value and the signal strength ofa neighboring cell (managed by same or a different eNB) is greater thana predefined second threshold value. Here, the first threshold value canbe less than the second threshold value. Event A5 triggering is expectedwhen the UE is moving out of the source cell and entering a neighboringcell. If the event A5 is detected, the neighboring cell (managed by sameor a different eNB) becomes the target eNB for a handover such that theUser Equipment (UE) detaches from the serving cell. Event A5 isapplicable for both intra-frequency and inter-frequency cells forrelative comparison.

Furthermore, in multi-carrier LTE i.e. LTE operation in carrieraggregation (CA) mode specified in LTE Release-10 specification, a newmeasurement event have been defined as Event A6 (intra-frequencyneighbor becomes offset better than Serving Cell, on secondary carrier).With this event, it is possible to evaluate the relative strength ofcells on a carrier, where the concerned carrier does not have to be theprimary carrier managed by the primary serving cell, or PCell. With thisevent, the network can make a cell change on the secondary LTE carrier.

According to 3GPP specification TS 36.300 for control plane (C-plane)architecture in dual connectivity there is no termination for the RRC(Radio Resource Control) protocol in the SeNB towards the UE. Ininter-eNB carrier aggregation employing dual connectivity, theconfiguration of cell(s) (carriers) that belongs to the SeNB can beprovided by the MeNB depending on data demand from the UE and the signalstrength of the SCG cells. The SCG cells are secondary cells (SCells)similar to SCells in Rel-10 CA. The UE needs to do synchronizationtowards the SCG cells since the SeNB is geographically separated. Sincethe RRC layer is only sitting in the MeNB, the MeNB is responsible forradio resource management and associated measurement configuration bothfor the MCG cells and SCG cells.

Similar to Rel-10 CA, for dual connectivity mode of operation of the UE,the primary cell (PCell) of the UE belongs to the MCG. UE can beconfigured with additional SCell(s) served by a set of frequencies inthe MCG. The set of frequencies handled by the MeNB are referred to as afirst set of frequencies. There can be at least one serving cell for theUE associated with a first serving frequency served by the MeNB. Withinthe SCG, the UE does not have PCell, but a cell having similarfunctionality like the PCell is configured to the UE. This special SCellwithin the SCG is called special SCell (pSCell or PSCell) where PUCCHresources are configured. The special SCell or PSCell in the SCGconfigured for the UE is used for transmission of HARQ feedback forPDSCH scheduled on SCG SCells and also the CQI reports for concerned SCGSCells over the configured PUCCH resources. UE can be configured withadditional SCell(s) in the SCG served by a set of frequencies differentfrom the first set of frequencies. The set of frequencies handled by theSeNB are called second set of frequencies. There is at least one servingcell for the UE associated with a second serving frequency served by theSeNB. Furthermore, the SCells within the MCG and SCG do not have PUCCH(Physical Uplink Control Channel) configuration but can provideadditional PUSCH resources to the UE. The configuration of pSCell/PSCellfor the UE within the SCG can be any of the configured SCells within theSCG. Assuming that SeNB is handling more than one SCell and each SCellon a different frequency, the Event A6 cannot be used for special SCell(pSCell/PSCell) change configured for the UE since Event A6 is onlyapplicable for intra-frequency measurements. Further, Events A2 andEvent A4 cannot be used because they cannot be used for relativecomparison of signal strength, they can be used only foraddition/removal of the carrier.

Furthermore, Events A3 and A5 cannot be used because currently theseevents are applicable only for the PCell. Hence in the above mentionedscenario for a UE configured with dual connectivity mode of operation,handling of special SCell (pSCell/PSCell) change cannot be done usingany of the above described events.

Therefore, for inter-eNB carrier aggregation i.e. dual connectivity modeof operation, the extension of measurement events A3 and A5 or newmeasurement event for relative inter-frequency comparison requires newRRC signaling between the UE and the MeNB.

When a plurality of Secondary Cells (SCell) are added simultaneously bythe MeNB during SCG establishment, there is a need to decide/determinespecific parameters of which SCell (i.e. a reference cell) are used forderiving a SeNB key by the MeNB. The indication of the reference SCelldecision/determination needs to be conveyed to the UE by the MeNB toenable the UE to derive the same SeNB key. A suitable entity should beconfigured to decide the reference cell namely the special SCell(pSCell) whose cell-specific parameters such as physical cell identity(PCI) and/or downlink frequency (DL-EARFCN) are to be used for KeNB keyderivation. The special SCell (pSCell or PSCell) seems a good candidateto be used as reference cell since the PSCell has some of the propertiesof primary cell (PCell) defined in 3GPP specification TS 36.300 and TS36.331.

The identification/determination or selection of pSCell/PSCell canaffect the SCG establishment and handover (HO) procedures involving theMeNB. The selection of the pSCell/PSCell is an issue that can requiresome coordination between MeNB and SeNB when making decision, whichSCell within the SCG can be the pSCell/PSCell. The RRM measurements fromthe UE indicate the relative radio link quality of the plurality ofSCells, which can be added during SCG establishment. The RRMmeasurements can be received from the UE through measurement report orsome feedback from the UE. In general it would be preferable for theSeNB to control the SCG configuration as much as possible; it can begood to consider how this objective could be realized.

The SeNB can decide the special SCell (pSCell/PSCell) from the pluralityof SCells added by the MeNB during SCG establishment. The SeNB canrandomly decide the pSCell/PSCell from the plurality of SCells added orthe SeNB can decide the pSCell/PSCell based on the physical resourceavailability i.e. taking the load information into account in theplurality of SCells.

If it is also required that the SeNB identified/determined or selectedpSCell/PSCell has to meet an additional radio link quality criterion,then the MeNB needs to be involved, as MeNB handles the RRM measurementsof the UE. The MeNB could assist the SeNB with measurement informationi.e. by providing the SeNB with a list of SCG cells meeting thepSCell/PSCell measurement criterion (i.e. the set of SCells from whichthe SeNB can make a selection of pSCell/PSCell based on resourceavailability).

Therefore, for inter-eNB carrier aggregation i.e. dual connectivity modeof operation, the assistance procedures by which one eNB provides eitherRRM measurement results or a list of candidate pSCell/PSCell, asdiscussed above, the information exchange is considered with newsignaling support on the X2 interface between the MeNB and SeNB.

Apart from this the SON (Self-Optimizing Network) related reports sentby the UE to network (eNB) are pertaining to the procedural reports andfailure reports of the PCell (MeNB) and not the pScell/PSCell (specialcell of SeNB). There is a need to enhance the existing reports for SON,which will provide information to SeNB through MeNB. The informationexchange is considered with new signaling support on the X2 interfacebetween the MeNB and SeNB.

In addition to this UE also need to provide UE capability to SeNB andalso there is need to define new Feature Group indicator (FGI) for SeNB.The UE can provide this information to the MeNB, which can be furthershared to the SeNB through the X2 interface.

The above information is presented as background information only tohelp the reader to understand the present invention. Applicants havemade no determination and make no assertion as to whether any of theabove might be applicable as Prior Art with regard to the presentapplication.

DISCLOSURE Technical Solution

The principal object of the embodiments herein is to provide a methodand system for selection of special SCell (pSCell/PSCell) by the SeNBfrom a plurality of SCells configured for a UE in the SCG.

Another object of invention is to provide a method and system forhandling of special SCell (pSCell/PSCell) change for a UE by extendingEvent A3 or Event A5 to pSCell/PSCell for relative comparison.

Another object of the invention is to provide enhancement in measurementby defining new functionalities for existing events.

Another object of the invention is to provide a method and system forhandling of special SCell (pSCell/PSCell) change for a UE withintroduction of a new Event Ax.

Another object of invention is to provide a method and system forinformation exchange related to RRM measurements on X2 interface toenable selection of best target pSCell/PSCell in case multiple SCellsconfigured for the UE have met the configured measurement events.

Another object of the invention is to provide a method and system tocontrol mobility by linking the multiple events configured for the UE toenable handling of special SCell (pSCell/PScell) in dual connectivityand handovers in Heterogeneous networks (HetNet) deployments.

Another object of the invention is to provide a method and system forinformation exchange related to Self-optimizing Network (SON) on X2interface to enable SON enhancements and new SON feature for dualconnectivity.

Another object of the invention is to provide the method to exchange ofUE capabilities between the MeNB and the SeNB over X2 interface anddefining new FGI bit for SeNB.

Accordingly the invention provides a method for managing selection of acell configured with Physical Uplink Control Channel (PUCCH) resourcesfor a User Equipment (UE) operating in a dual connectivity mode ofoperation in a wireless communication network, the wirelesscommunication network comprising of a first evolved NodeB (eNB)connected to a second eNB by an X2 interface, the method comprisingsending a Radio Resource Control (RRC) message for measurementconfiguration by the first eNB to the UE for at least one configuredfrequency, wherein the configured frequency is distinct from at leastone first serving frequency served by the first eNB; evaluatingmeasurement events by the UE based on the measurement configuration;sending radio resource management (RRM) measurement results to the firsteNB by the UE on at least one the configured measurement event beingtriggered for the at least one the configured frequency apart from theat least one first serving frequency served by the first eNB wherein theRRM measurement results comprises at least one of Reference SignalReceived Power (RSRP) and Reference Signal Received Quality (RSRQ); andinitiating a procedure towards the second eNB by the first eNB forconfiguring the UE with dual connectivity mode of operation over the X2interface with at least one second serving frequency to be served by thesecond eNB based on the RRM measurement results for the at least one theconfigured frequency received from the UE apart from the at least onefirst serving frequency served by the first eNB.

Accordingly provided herein is a wireless communication networkcomprising of a first evolved NodeB (eNB) connected to a second eNB byan X2 interface and at least one User Equipment (UE), configured formanaging selection of a cell configured with Physical Uplink ControlChannel (PUCCH) resources for the User Equipment (UE) operating in adual connectivity mode of operation in the wireless communicationnetwork, wherein the first eNB is configured for sending a RadioResource Control (RRC) message for measurement configuration to the UEfor at least one configured frequency, wherein the configured frequencyis distinct from at least one first serving frequency served by thefirst eNB; the UE configured for evaluating measurement events based onthe measurement configuration; and sending radio resource management(RRM) measurement results to the first eNB on at least one theconfigured measurement event being triggered for the at least one theconfigured frequency apart from the at least one first serving frequencyserved by the first eNB wherein the RRM measurement results comprises atleast one of Reference Signal Received Power (RSRP) and Reference SignalReceived Quality (RSRQ); and the first eNB further configured forinitiating a procedure towards the second eNB for configuring the UEwith dual connectivity mode of operation over the X2 interface with atleast one second serving frequency to be served by the second eNB basedon the RRM measurement results for the at least one the configuredfrequency received from the UE apart from the at least one first servingfrequency served by the first eNB.

Accordingly provided herein is a first evolved NodeB (eNB) in a wirelesscommunication network, wherein the first eNodeB is connected to a secondeNB by an X2 interface and at least one User Equipment (UE) and the UserEquipment (UE) is operating in a dual connectivity mode of operation inthe wireless communication network, the first eNB configured for sendinga Radio Resource Control (RRC) message for measurement configuration tothe UE for at least one configured frequency, wherein the configuredfrequency is distinct from at least one first serving frequency servedby the first eNB; initiating a procedure towards the second eNB forconfiguring the UE with dual connectivity mode of operation over the X2interface with at least one second serving frequency to be served by thesecond eNB based on radio resource management (RRM) measurement resultsfor the at least one configured frequency received from the UE apartfrom the at least one first serving frequency served by the first eNB,wherein the RRM measurement results are received from the UE on at leastone configured measurement event being triggered for the at least onethe configured frequency apart from the at least one first servingfrequency served by the first eNB and the RRM measurement resultscomprises at least one of Reference Signal Received Power (RSRP) andReference Signal Received Quality (RSRQ).

Provided herein is a second evolved NodeB (eNB) in a wirelesscommunication network, wherein the second eNodeB is connected to a firsteNB by an X2 interface and at least one User Equipment (UE) and the UserEquipment (UE) is operating in a dual connectivity mode of operation inthe wireless communication network, the second eNB configured forreceiving a procedure from the first eNB for configuring the UE withdual connectivity mode of operation over the X2 interface with at leastone second serving frequency to be served by the second eNB based onradio resource management (RRM) measurement results for the at least oneconfigured frequency received from the UE apart from the at least onefirst serving frequency served by the first eNB, wherein the RRMmeasurement results are received from the UE on at least one configuredmeasurement event being triggered for the at least one the configuredfrequency apart from the at least one first serving frequency served bythe first eNB wherein the RRM measurement results comprises at least oneof Reference Signal Received Power (RSRP) and Reference Signal ReceivedQuality (RSRQ).

Provided herein is a User Equipment connected to a wirelesscommunication network, the wireless communication network comprising ofa first evolved NodeB (eNB) connected to a second eNB by an X2 interfaceand the User Equipment (UE) is operating in a dual connectivity mode ofoperation in the wireless communication network, the UE furtherconfigured for receiving a Radio Resource Control (RRC) message formeasurement configuration from the first eNodeB for at least oneconfigured frequency, wherein the configured frequency is distinct fromat least one first serving frequency served by the first eNB; evaluatingmeasurement events based on the measurement configuration; sending radioresource management (RRM) measurement results to the first eNB on atleast one the configured measurement event being triggered for the atleast one the configured frequency apart from the at least one firstserving frequency served by the first eNB wherein the RRM measurementresults comprises at least one of Reference Signal Received Power (RSRP)and Reference Signal Received Quality (RSRQ); and receiving a RRCconnection reconfiguration message from the first eNB for configuringthe UE for the dual connectivity mode of operation comprisingconfiguration for at least one second serving frequency served by thesecond eNB including information concerning the serving cell configuredwith the PUCCH resources on at most one the second serving frequency forthe UE.

These and other aspects of the embodiments herein will be betterappreciated and understood when considered in conjunction with thefollowing description and the accompanying drawings. It should beunderstood, however, that the following descriptions, while indicatingpreferred embodiments and numerous specific details thereof, are givenby way of illustration and not of limitation. Many changes andmodifications can be made within the scope of the embodiments hereinwithout departing from the spirit thereof, and the embodiments hereininclude all such modifications.

DESCRIPTION OF DRAWINGS

This invention is illustrated in the accompanying drawings, throughoutwhich like reference letters indicate corresponding parts in the variousfigures. The embodiments herein will be better understood from thefollowing description with reference to the drawings, in which:

FIG. 1 is a block diagram illustrating an inter-evolved node B (eNB)carrier aggregation in a wireless communication network system such asthat of 3GPP's Long Term Evolution (LTE), according to embodiments asdisclosed herein;

FIGS. 2a and 2b illustrate the user plane architecture options at thenodes involved in dual connectivity mode of operation;

FIGS. 3a and 3b are flow diagrams illustrating an exemplary process ofperforming selection of a cell configured with Physical Uplink ControlChannel (PUCCH) resources for the UE operating in a dual connectivitymode of operation, according to embodiments as disclosed herein;

FIG. 4 is a flowchart illustrating the UE operation for performingmeasurement event evaluation for a serving cell configured with PhysicalUplink Control Channel (PUCCH) resources including plurality of MCG andSCG SCells when said UE is operating in a dual connectivity mode ofoperation, according to embodiments as disclosed herein;

FIGS. 5a and 5b are flowcharts illustrating the MeNB operation forconfiguring the UE to operate in a dual connectivity mode of operation,according to embodiments as disclosed herein;

FIGS. 6a and 6b are flowcharts illustrating the SeNB operation forperforming selection of a serving cell for a UE to be configured withPhysical Uplink Control Channel (PUCCH) resources from a plurality ofSCG SCells when said UE is configured to operate in a dual connectivitymode of operation, according to embodiments as disclosed herein;

FIG. 7 depicts the reason as to why Event A3 and Event A5 are requiredto be modified;

FIGS. 8a and 8b illustrates a method to extend the applicability ofevents A3 and A5 to PCell or PSCell using a modified reportingconfiguration (having a new information element or a flag indication thecell group i.e. whether the event is evaluated for PCell or PSCell),according to the embodiments as disclosed herein;

FIGS. 9a and 9b illustrate alternate methods to extend applicability ofevents A3 and A5 to PCell and PSCell, according to embodiments asdisclosed herein;

FIGS. 10a and 10b illustrate methods for independent triggering ofmeasurement events based on absolute thresholds and an example scenariowhen TTT is running for configured measurement events associated withcorresponding measurement Ids;

FIGS. 11a, 11b and 11c illustrate methods for linking of measurementevents based on absolute thresholds and example scenarios when the TTTis expired for only one configured measurement event but reporting isdone for linked measurement events associated with correspondingmeasurement IDs, according to embodiments as disclosed herein;

FIG. 12 illustrate flowcharts explaining sequence of procedures involvedat the UE when measurement linking between multiple measurement ids orevents is signaled/initiated, according to embodiments as disclosedherein;

FIG. 13 illustrates an example scenario of network decisions whenmeasurement report is sent to network after satisfying the criteria forevent A1, A2 or A4, according to embodiments as disclosed herein;

FIG. 14 illustrates an example scenario of network decisions whenmeasurement report is sent to network after meeting the leaving criteriafor event A1, A2 or A4, according to embodiments as disclosed herein;

FIG. 15 illustrates a block diagram of the eNB (which can be at leastone of the MeNB or SeNB), according to embodiments as disclosed herein;and

FIG. 16 illustrates a block diagram of the UE, according to embodimentsas disclosed herein.

MODE FOR INVENTION

The embodiments herein and the various features and advantageous detailsthereof are explained more fully with reference to the non-limitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. Descriptions of well-knowncomponents and processing techniques are omitted so as to notunnecessarily obscure the embodiments herein. Also, the variousembodiments described herein are not necessarily mutually exclusive, assome embodiments can be combined with one or more other embodiments toform new embodiments. The examples used herein are intended merely tofacilitate an understanding of ways in which the embodiments herein canbe practiced and to further enable those of skill in the art to practicethe embodiments herein. Accordingly, the examples should not beconstrued as limiting the scope of the embodiments herein.

The terms “first evolved Node B” (first eNB), “Master eNB (MeNB)”,“primary eNB”, and “anchor eNB” have been used interchangeably hereinand can refer to a single eNB, which connects a User Equipment (UE) tothe core network (which terminates at least S1-MME interface). A groupof cells handled by the MeNB is referred to herein as Master Cell Group(MCG).

Throughout the document, the terms “second eNB”, “Secondary eNB (SeNB)”,“small eNB”, “slave eNB” and “Drift eNB” have been used interchangeablyand the terms can refer to an eNB that serves the UE to enhance datathroughput at the UE (but not the MeNB). A group of cells handled by theSeNB is referred to herein as Secondary Cell Group (SCG).

Throughout the document, the term “serving cell configured with PUCCHresources”, “Special SCell”, “PSCell” and “pSCell” have been usedinterchangeably and can refer to at most one SCell from a plurality ofSCG SCells served by the SeNB.

Embodiments herein provide a method and system for selection of aspecial SCell (pSCell/PSCell) by the SeNB from a plurality of SCellsconfigured for a UE in the SCG. Information exchange related to radioresource management (RRM) measurements on X2 interface when multipleSCells configured for the UE have met the configured measurement eventsis provided to enable selection of best target pSCell/PSCell.

In an embodiment, the SeNB determines/selects the PSCell from theplurality of SCells added by the MeNB during SCG establishment. The SeNBcan randomly decide the PSCell from the plurality of SCells added or theSeNB can decide the PSCell based on the physical resource availabilityi.e. taking the load information into account in the plurality ofSCells.

In an embodiment, if it is also required that the SeNBidentified/determined or selected PSCell has to meet an additional radiolink quality criterion, then the MeNB handles the RRM measurements ofthe UE. The MeNB can assist the SeNB with measurement information, i.e.by providing the SeNB with a list of SCG cells meeting the PSCellmeasurement criterion (i.e. the set of SCells from which the SeNB canmake a selection of PSCell based on resource availability i.e. takingthe load information into account in the plurality of SCells).

Embodiments herein provide a method and system for handling of specialSCell (PSCell) change by extending Event A3 or Event A5 to PSCell. EventA3 and A5 are extended for special SCell, such that it can be used tochange and/or determine the current Special SCell of SeNB from aplurality of SCG SCells. Further, the method and system provideshandling of special SCell (PSCell) change with a new Event Ax definedfor relative comparison of inter-frequency measurements.

In an embodiment, a measurement report triggered by an Event Ax (i.e. anevent for inter-frequency comparison) indicates to network that a newcomponent carrier (CC) within the SCG is better than the special SCelland that this new cell (CC) can now be made as the new special SCell.The network can further change the special cell of SeNB based on thisevent.

Embodiments herein also provide SON enhancements for dual connectivity,linking of multiple events and enhanced functionality for the existingevents.

Referring now to the drawings, and more particularly to FIGS. 1 through16, where similar reference characters denote corresponding featuresconsistently throughout the figures, there are shown preferredembodiments.

FIG. 1 is a block diagram illustrating an inter-evolved node B (eNB)carrier aggregation in a wireless communication network system 100 suchas that of 3GPP's Long Term Evolution (LTE), according to embodiments asdisclosed herein. The wireless communication network system 100 includesa Mobility Management Entity (MME) 102, a first eNB (MeNB) 104, a secondeNB (SeNB) 106, and a User Equipment (UE) 108 with inter-eNB carrieraggregation. The MME 102 manages session states, authentication, paging,mobility with 3GPP, 2G and 3G nodes, roaming, and other bearermanagement functions. The UE 108 can be a mobile phone, a tablet, awearable computing device, a communication dongle or any other devicecapable of connecting and communicating over a wireless communicationnetwork system 100. The UE 108 can be capable of operating in a dualconnectivity mode of operation simultaneously connected to the MeNB 104and the SeNB 106.

The MeNB 104 can be a macro eNB, a primary eNB, a first eNB, a anchoreNB or any other eNB capable of being a part of a wireless communicationnetwork system 100 and serving at least one cell served on a firstcarrier frequency (F1) to the UE 108. The SeNB 106 can be a secondaryeNB, a small eNB, a drift eNB or any other eNB capable of being a partof a wireless communication network system 100 and serving at least onecell served on a second carrier frequency (F2) to the UE 108. The MeNB104 and SeNB 106 can be parts of the same wireless communication networksystem 100 and can be connected to each other at the backend through anon-ideal backhaul such as X2 interface 110 and communicate using the X2application protocol (X2-AP). The UE 108 can be configured to connect toat least one of the MeNB 104 and SeNB 106 using suitable air interfaces.There can be a plurality of SeNBs and MeNBs present in the wirelesscommunication network system 100. The wireless network system 100 isonly one example of a suitable environment and is not intended tosuggest any limitation as to the scope of use or functionality of theinvention.

In an embodiment, the MeNB 104 is connected to the SeNB 106 with aninterface characterized by one of a non-ideal backhaul link and an idealbackhaul link. The UE 108 is carrier aggregated with at least one firstserving frequency (F1) served by the MeNB 104 and at least one secondserving frequency (F2) served by the SeNB 106 and configured to operatein dual connectivity mode of operation in at least one of a downlinkdirection and an uplink direction with the MeNB 104 and the SeNB 106. Inan embodiment, the wireless network system uses a set of data radiobearers (DRBs) for the UE 108 that is transmitted over the MeNB 104,while another set of data radio bearers (DRBs) for the UE 108 istransmitted over the SeNB 106. When the MeNB 104 and the SeNB 106 servethe UE 108, the MeNB 104 handles the control plane 112 of the UE 108,while the user plane or data plane 114 and 116 handling of the UE 108gets either distributed or split between the MeNB 104 and the SeNB 106.

FIG. 2 illustrates protocol architectures for dual connectivity underconsideration in 3GPP specification TR 36.842, according to embodimentsas disclosed herein. The FIG. 2a illustrates a core network (CN) splitarchitecture from eNB perspective, according to embodiments as disclosedherein. As shown in the FIG. 2a , the S1-U terminates at the MeNB 104and the SeNB 106. This architecture is referred as core network (CN)split where a set of Evolved Packet System (EPS) bearers of the UE 108are split in the core network at the Service-Gateway (S-GW) and the EPSbearers are mapped on the respective S1-U interfaces towards the MeNB104 and the SeNB 106. The respective EPS bearers are mapped on tocorresponding data radio bearers (DRBs) of the MeNB 104 and the SeNB106.

The FIG. 2b illustrates Radio Access Network (RAN) split architecturefrom eNB perspective, according to embodiments as disclosed herein. Asshown in the FIG. 2b , the S1-U terminates only at the MeNB 104. Thisarchitecture is referred as radio access network (RAN) split where theEPS bearer #2 of the UE 108 is split in the MeNB 104 and the offloadedbearer is mapped on the X2 interface 110 towards the SeNB 106. The layer2 protocol stack for the data radio bearer associated with the MeNB 104(EPS Bearer #1 and Split EPS Bearer #2) and the SeNB 106 (Offloaded EPSBearer #2) includes an independent PDCP entity per bearer at the MeNB104, an independent Radio Link Control (RLC entity) per bearer at theMeNB 104 and the SeNB 106, and a common Medium Access Control (MAC)entity at the MeNB 104 and an independent MAC entity at the SeNB 106.The split/offloaded data radio bearer associated with the MeNB 104 (EPSBearer #2) and also associated with the SeNB 106 can be handled by thePDCP entity associated with MeNB 104 called the common PDCP entity.Further, the MeNB 104 includes an RRC protocol for control signaling112. The layer 2 protocol stack associated with the MeNB 104 and theSeNB 106 for handling the data radio bearers associated with the MeNB104 and the SeNB 106 which includes the MAC entity, the RLC entity, andthe PDCP entity as shown in FIG. 2a and FIG. 2b is also duplicated atthe UE 108 from the UE perspective and hence not shown explicitly forsimplicity.

FIGS. 3a and 3b are flow diagrams illustrating an exemplary process ofperforming selection of PSCell i.e. a cell configured with PhysicalUplink Control Channel (PUCCH) resources for the UE operating in a dualconnectivity mode of operation, according to embodiments as disclosedherein. At step 310, the UE 108 establishes RRC connection with the MeNB104 and UE 108. The UE 108 performs user plane data exchange with theMeNB 104 on the data radio bearers established by the MeNB 104 i.e. theMCG bearer(s) handle the data. The UE 108 performs RRM measurements atleast one of Reference Signal Received Power (RSRP) and Received SignalReceived Quality (RSRQ) for plurality of frequencies, which have beenconfigured at the UE 108 based on the measurement configuration providedby the MeNB 104 in step 301. The MeNB 104 receives the RRM measurementsfor a plurality of frequencies from the UE 108 at step 302. Theplurality of configured frequencies include the serving cell(s)associated with a first set of frequencies served by the MeNB 104 andneighbor cell(s) associated with a second set of frequencies served bythe SeNB 106, wherein frequencies in the first set and second set canbelong to the same band or can belong to different bands. There is atleast one cell served by the MeNB 104 served by a first frequency andthe cell on which the UE establishes the RRC connection in step 301 iscalled the PCell of the UE 108. The other cells configured for the UE108 handled by the MeNB 104 are secondary cells (SCells) and henceforthreferred as Master Cell Group (MCG) including the PCell. Based on thereceived measurement results for the second set of frequencies and ifthe data demand for the UE 108 increases then, the MeNB 104 makes adecision on whether to add an SeNB 106 with at least one SCellassociated with a second frequency served by the SeNB 106. The SeNB 106is added on the MeNB 104 making a decision to add SeNB 106 by sending anadd request X2 message to the SeNB 106 on the X2 interface 110, as instep 303. In an embodiment herein, the MeNB 104 can add multiple SCells,including the corresponding RRM measurements associated with addedSCells. Based on the received add request if the X2 message includesonly one SCell then, the SeNB 106 by default decides the added SCell asthe PSCell for the UE 108 at step 304. In an embodiment herein, ifmultiple SCells are received in the add request message then, the SeNB106 decides the PSCell for the UE 108 from the second set of frequenciesbased on the associated RRM measurement results (received in a X2message from the MeNB 104 over the X2 interface) and load information(i.e. physical resource availability for PUCCH) associated with the setof frequencies assessed by the SeNB 106. In yet another embodiment, theSeNB 106 can also determine the PSCell for the UE 108 in a randommanner. In one example the determination is from the plurality of SCGSCells such that PUCCH load is uniformly distributed across the SCGSCells for the UE population density served by the SeNB 106. There canbe at least one cell served by the SeNB 106 served by a second frequencyand the cell on which the PUCCH resources are configured for the UE 108is called the PSCell of the UE. The other cells configured for the UE108 handled by the SeNB 106 are secondary cells (SCells) and henceforthreferred as Secondary Cell Group (SCG) including the PSCell. On decidingthe PSCell to be configured to the UE 108, the SeNB 106 sends an addresponse to the MeNB 104 over the X2 interface at step 305, wherein theadd response comprises of configuration information related to thePSCell such as PUCCH configuration and E-UTRA Absolute Radio FrequencyChannel Number (EARFCN) associated with the PSCell and other SCells andtheir corresponding EARFCNs served by the SeNB 106. In an embodimentherein, the response message comprises configuration for at least onesecond serving frequency served by the SeNB 106 including informationconcerning the serving cell configured with the PUCCH resources on atmost one second serving frequency for the UE 108. On receiving the addresponse from the SeNB 106, at step 306 the MeNB 104 sends an X2 messagewith acknowledgement to the SeNB 106. The MeNB 104 derives the securitybase key associated with SeNB 106 for UE 108 using at least one of afreshness parameter (i.e. SCG Counter) and cell-specific parameters ofthe PSCell. The acknowledgement message 306 includes the security basekey associated with the SeNB 106 for the UE 108, derived by the MeNB104. The MeNB 104 sends a RRC Connection Reconfiguration message 307 tothe UE 108, wherein the Reconfiguration message comprises of informationrelated to at least the PSCell configuration, SCG Counter (SCC),configuration of other SCells added, measurement configurations and soon. In an embodiment herein, the RRC connection reconfiguration messagecomprises configuration for at least one second serving frequency servedby the SeNB 106 including information concerning the serving cellconfigured with the PUCCH resources on at most one second servingfrequency for the UE 108. In an embodiment herein, the RRC connectionreconfiguration message further comprises the measurement configurationfor the UE 108 for at least one first serving frequency served by theMeNB 104 and at least one said second serving frequency served by theSeNB 106 wherein the measurement configuration includes at least one ofa measurement event based on an A3 event, an A5 event, an Ax event, anindication for linking of measurement identities, a report on leave flagin the reportConfigEUTRA for the measurement event based on an A1 event,an A2 event and an A4 event and so on. The MeNB 104 can either triggerthe DRB path switch procedure towards the core network (CN) foroffloading the MCG bearer to the SeNB 106 or establishing new data radiobearers (DRBs) on the SeNB 106. At steps 308 a and 308 b for offloadedMCG bearer the MeNB 104 also sends the SN status count and performs dataforwarding to the SeNB 106. At the UE side on comprehending thereconfiguration received in step 307, the UE 108 sends a RRC ConnectionReconfiguration complete message to the MeNB 104 confirming the SCGestablishment. At step 310, the UE 108 performs Random access procedureon the PSCell of SeNB 106 for uplink synchronization with the SeNB 106.After the random access procedure is successful, the UE 108 derives thesecurity base key associated with SeNB 106 using at least one of SCC andcell-specific parameters of the PSCell. At step 311, the DRBs areestablished on the SCG SCells and secure data exchange between the SeNB106 and UE 108 configured in dual connectivity mode of operation ishandled by the SCG data bearer(s).

At step 312, the UE 108 evaluates measurement events for plurality ofconfigured frequencies (i.e. including MCG and SCG cells), based on themeasurement configuration received in step 307. The RRM measurementresults can be sent on a trigger of a configured event being detected bythe UE 108 (such as a modified measurement event, the Ax event and soon). The measurement report comprising the RRM measurement resultsassociated with the PCell, PSCell, other S cells and so on can be sentin step 313 by the UE 108 to the MeNB 104 (i.e. to the PCell of the MeNB104). The measurement results further comprises of at least one of RSRPand RSRQ. At step 314, on the MeNB 104 receiving the RRM measurementresults associated with the MCG and SCG, the MeNB 104 makes a decisionon whether the SeNB configuration for the UE 108 needs to be modified.The decision can be based on the measurement results for anotherconfigured frequency associated with the SeNB currently not serving theUE and/or neighbor cell measurements for cells served by another SeNBand/or a first serving frequency served by the MeNB 104. At step 315,the MeNB 104 initiates a procedure towards the SeNB 106 to modify theSeNB configuration for UE 108. In an embodiment herein, the MeNB 104further provides the RRM measurement results concerning at least onesecond serving frequency served by the SeNB 106 for the UE 108 and/orconcerning at least one configured frequency for the UE 108 apart fromthe set of second serving frequencies served by the SeNB 106 for the UE108. Based on the RRM measurement results received in step 315, the SeNB106 determines if the current PSCell for the UE 108 is to be changedtaking the new information as one of the input parameter. However, theavailability of the latest measurement results concerning the currentPSCell is optional for the PSCell change decision-making process at theSeNB 106. In an embodiment herein, the SeNB determines if the currentPSCell is to be changed based on the RRM measurement results concerningthe second frequency associated with the current serving cell configuredwith the PUCCH resources and/or load information (i.e. physical resourceavailability) associated with the current serving cell configured withthe PUCCH resources and so on. If the current PSCell for the UE 108 doesnot need to be changed, the SeNB 106 retains the current PSCell. If thecurrent PSCell needs to be changed, the SeNB 106 determines a PSCell,based on a plurality of factors. The plurality of factors can compriseof the second serving frequency of current PSCell served by the SeNB 106based on the received RRM measurement results not suitable from radiolink quality point of view and/or received RRM measurement results forthe set of second serving frequencies excluding the PSCell frequency butincluding measurement results for additional configured frequency to bebetter than measurement results for current PSCell and the loadinformation (i.e. physical resource availability) assessed by the SeNB106 for the current serving cell configured with the PUCCH resourcesand/or other SCG SCells. On performing the PSCell change, the SeNB 106sends an indication about the PSCell change to the MeNB 104 at step 318.In an embodiment herein, the indication comprises of a cause valuePSCell change in a X2 message over the X2 interface towards the MeNB104. At step 319, the MeNB 104 further, verifies if there is a change inthe current PSCell of the UE 108. If there is no change in the PSCell,the MeNB 104 does not perform any further related actions. If there is achange in the PSCell of the UE 108, in response, the MeNB 104 sends theupdated SeNB key for the UE to the SeNB 106 at step 320. Towards the UE108 the MeNB 104 sends a RRC Reconfiguration message at step 321,wherein the Reconfiguration message comprises of information related toat least the configuration of the new PSCell and the SCG counter (SCC)to enable the UE 108 to derive the update security base key associatedwith the SeNB 106.

In an embodiment herein, the UE 108 sends the RRM measurement results tothe MeNB 104 for the one configured frequency and the another configuredfrequency when at least one of the measurement event associated with themeasurement object being triggered and the indication for linking ofmeasurement identities associated with a side condition is received inthe reportConfigEUTRA by the UE 108.

In an embodiment herein, the pSCell/PSCell identification/selectiondetermined by the SeNB 106 seems reasonable since the SeNB 106 can takethe availability of e.g. PUCCH resources into account i.e. loadinformation or physical resource availability. In another embodiment, ifthe SeNB identified/selected pSCell/PSCell has to meet an additionalradio link quality criterion, then the MeNB 104 needs to be involvedsince the MeNB handles the RRM measurements of the UE. The MeNB 104 canassist the SeNB 106 with measurement information by providing the SeNB106 with a list of SCG cells meeting the pSCell/PSCell measurementcriterion and/or forward the RRM measurement results for the set ofSCells from which the SeNB can make a selection of pSCell/PSCell basedon PUCCH resource availability i.e. load information).

In an embodiment herein, the assistance procedures by which one eNBprovides a list of candidate pCells/PSCells and/or RRM measurementresults for SCG SCells, as discussed above, the information exchange isconsidered being a slow scale interaction procedure i.e. the assistanceinformation would be provided only if there is a real need.

For the assistance information exchange between MeNB and SeNB forpSCell/PSCell identification and selection, the general principleapplied in this invention is that if SeNB 106 is deciding thepSCell/PSCell then MeNB 104 provides the RRM measurements of the UE fora list of SCells and the SeNB 106 decides the pSCell/PSCell based on RRMmeasurement results and/or physical resource availability i.e. loadinformation/PUCCH resource availability.

FIG. 4 is a flowchart illustrating the UE operations for performingmeasurement event evaluation for a serving cell configured with PhysicalUplink Control Channel (PUCCH) resources including plurality of MCG andSCG SCells when said UE is operating in a dual connectivity mode ofoperation, according to embodiments as disclosed herein. On establishingRRC connection on the PCell of the MeNB 104, the UE 108 performs RRMmeasurements for plurality of configured frequencies based on thereceived measurement configuration. The UE 108 sends (401) the RRMmeasurement report to the PCell of the MeNB 104 when at least one of themeasurement event associated with plurality of configured frequenciesgets triggered. On a new SeNB 106 being added, the UE 108 receives (402)a RRC Connection Reconfiguration message for a SCG establishment fromthe MeNB 104. The Reconfiguration message comprises of informationrelated to at least the PSCell configuration i.e. the serving cellconfigured with PUCCH resources for the UE, one or more SCG SCellsadded, SCG counter (SCC), measurement configurations and so on. Based onthe reconfiguration message, the UE can comprehend with the newconfiguration related to SCG establishment. On comprehending thereconfiguration, the UE 108 sends (403) a RRC Connection Reconfigurationcomplete message to the MeNB 104 indicating that the UE 108 has appliedthe configuration associated with the SeNB 106. The UE 108 then performs(404) the Random Access (RA) procedure on the cell configured with PUCCHresources for the UE 108 to get uplink synchronized on at least thePSCell served one of the frequencies belonging to the second set offrequencies associated with the SeNB 106. The UE 108 check (405) if theRandom Access (RA) procedure on the PSCell served by the SeNB 106 issuccessful. If the RA procedure is successful, then the UE 108 derives(406) the security base key associated with SeNB 106 based on at leastone of SCC and cell-specific parameters of the PSCell. The UE 108further establishes the L2 user plane protocol stack i.e. SCG MAC entityand RLC and PDCP entity for the data radio bearers associated with theSeNB 106. Using the security base key associated with the SeNB 106, dataexchange is now possible for the SCG DRBs between the UE 108 and SeNB106. Also, data exchange continues for the MCG DRBs between the UE 108and MeNB 104 applying the security base key associated with the MeNB104. Since the UE 108 is mobile, the UE 108 continuously evaluates (407)the measurement events, according to the measurement configuration asreceived in the RRC reconfiguration message. The measurementconfiguration includes one or more measurement objects, one or moremeasurement identities and one or more reporting configurations. Eachmeasurement object can be associated with the corresponding frequencyserved by the MeNB 104 or the SeNB 106. The reporting configurationcomprises the measurement events such as the A3, A5 events and so on.The measurement identity links the measurement object and the reportingconfiguration. In an embodiment herein, if the event A3 and/or event A5is configured in the reporting configuration then either the measurementobject or the reporting configuration is extended with a flag indicatingwhether the event is applicable to the PCell of the MeNB 104 or thePSCell of the SeNB 106. Alternately the measurement configurationcomprising more than on measurement identities can be linked with a flagin the reporting configuration, as depicted in FIGS. 11b and 11c . Ondetecting (407) the triggering of the measurement event, the UE 108sends (408) measurement results to the PCell of the MeNB 104 associatedwith serving cells and neighbor cells served by plurality of configuredfrequencies for the UE. The measurement results comprise of RRMmeasurement results for PCell of the UE 108 associated with MeNB 104,the PSCell of the UE 108 associated with SeNB 106, other MCG and SCGSCells and so on. The measurement results further comprises of at leastone of Reference Signal Received Power (RSRP) and Received SignalReceived Quality (RSRQ). After sending the RRM measurement results theUE 108 can expect a further RRC reconfiguration message from the MeNB104. At step 405, if it detected that the random access procedure hasfailed then the UE 108 reports (409) the same to the PCell associatedwith the MeNB 104. The various actions in method 400 can be performed inthe order presented, in a different order or simultaneously. Further, insome embodiments, some actions listed in FIG. 4 can be omitted.

FIGS. 5a and 5b are flowcharts illustrating the MeNB operation forconfiguring the UE to operate in a dual connectivity mode of operation,according to embodiments as disclosed herein. The UE 108 is connected tothe PCell associated with the MeNB 104 after establishing the RRCconnection. The MeNB 104 can be connected to one or multiple SeNBsthrough X2 interface.

The MeNB 104 receives (501) the measurement reports/results forplurality of configured frequencies from the UE 108, on the criteria forconfigured measurement event being satisfied or triggered at the UEside. Based on the received measurement results and if the data demandfor the UE 108 is high, the MeNB 104 checks (502) if a suitable SeNBfrom a plurality of SeNBs connected through X2 interface to the MeNB 104can be added. Once the MeNB 104 decides to add the SeNB 106, the MeNB104 sends (503) an add request comprising of a plurality of SCells tothe SeNB 106 over the X2 interface along with the associated RRMmeasurements sent by the UE 108. In response the MeNB 104 receives anadd response message (504) from the SeNB 106, wherein the add responsecomprises of information related to the PSCell and other SCellsassociated with the SeNB 106. The response message comprises the SCGconfiguration, which includes at least the PSCell configuration i.e. theserving cell, configured with PUCCH resources for the UE, and optionallyplurality of SCells associated with SeNB 106. On receiving (504) the addresponse from the SeNB 106, the MeNB 104 approves the received SCGconfiguration sent by the SeNB 106. The MeNB 104 derives the securitybase key of the UE 108 associated with the SeNB 106 based at least oneof SCG counter and cell-specific parameters of the PSCell. The MeNB 104sends (505) an acknowledgement to the SeNB 106, which comprises thesecurity based key for the UE 108 associated with SeNB 106. The MeNB 104sends (506) a RRC Connection Reconfiguration message to the UE 108,wherein the Reconfiguration message comprises of information related toat least the PSCell configuration i.e. the serving cell configured withPUCCH resources for the UE, one or more SCG SCells added, SCG counter(SCC), measurement configurations and so on. The MeNB 104 receives (507)a RRC Connection Reconfiguration complete message from the UE 108 on theUE 108 comprehending the reconfiguration sent in (506) indicating to theMeNB 104 that it has applied the configuration associated with the SeNB106. The MeNB 104 checks (508) if the UE has sent a Random Access (RA)report to the PCell associated with the MeNB 104 indicating that the UEfailed to uplink synchronize on the PSCell associated with the SeNB 106.If the MeNB 104 does not receive the RA failure report from the UE 108then it is assumed that RA procedure on the PSCell associated with theSeNB 106 is successful. The MeNB 104 sends the SN status count andperforms (509) data forwarding to the SeNB 106 and starts the pathswitch procedure towards the core network (CN) to offload the MCG bearerto the SeNB 106. With this procedure the offloaded bearers areestablished on the SeNB 106 and the UE 108 starts operating in dualconnectivity mode of operation with the MeNB 104 and SeNB 106. Further,the MeNB 104 receives (510) measurement results from the UE 108 as theUE 108 continuously evaluates the measurement events, according to themeasurement configuration received in the RRC reconfiguration message(as in 506). The measurement results comprise of RRM measurement resultsfor PCell associated with MeNB 104, PSCell associated with SeNB 106,other MCG and SCG SCells and so on. The measurement results furthercomprises of at least one of Reference Signal Received Power (RSRP) andReceived Signal Received Quality (RSRQ). On the MeNB 104 receiving themeasurement results, the MeNB 104 checks (511) whether the SeNBconfiguration for the UE 108 needs to be changed. In an example, thedecision can be based the measurement results for a configured frequencycurrently not served by the SeNB 106 to the UE 108 is better than athreshold and can be added as an SCG SCell to the UE 108. On deciding(511) to change the SeNB configuration for the UE 108, the MeNB 104initiates (512) a procedure to the SeNB 106 to modify the SeNB 106 overthe X2 interface by sending a modification message. In an embodimentherein, the modification message can include either the RRM measurementssent by the UE 108 associated with plurality of SCG SCells and/or newSCG SCell decided to be added by the MeNB 104. Alternately the MeNB 104can provide to the SeNB 106 with a list of SCG cells in the modificationmessage meeting the PSCell measurement criterion. On receiving (512) anindication from the SeNB 106 about the PSCell change, the MeNB 104checks (514) whether the configuration for PSCell provided by SeNB 106is different from the current configured PSCell for the UE 108. In casePSCell for the UE 108 has changed or modified then the MeNB 104 sends(515) the updated SeNB key of the UE to the SeNB 106. Also MeNB 104sends (516) a RRC Reconfiguration message to the UE 108, wherein theReconfiguration message comprises of information related to theconfiguration of the new or modified PSCell i.e. the serving cellconfigured with PUCCH resources for the UE, one or more SCG SCellsadded, SCG counter (SCC), measurement configurations and so on. Theprocess control then moves back to step 507 where the MeNB 104 receivesRRC reconfiguration complete message from the UE 108. The variousactions in method 500 can be performed in the order presented, in adifferent order or simultaneously. Further, in some embodiments, someactions listed in FIGS. 5a and 5b can be omitted.

FIGS. 6a and 6b is a flowchart illustrating the SeNB operation forperforming selection of a serving cell for a UE to be configured withPhysical Uplink Control Channel (PUCCH) resources from a plurality ofSCG SCells when said UE operates in a dual connectivity mode ofoperation, according to embodiments as disclosed herein. The UE 108 isconnected to the PCell associated with the MeNB 104 after establishingthe RRC connection. The MeNB 104 can be connected to one or multipleSeNBs through the X2 interface. Based on the received measurementresults from the UE and if the data demand for the UE 108 is high, theMeNB 104 decides to add the SeNB 106. The SeNB 106 receives (601) an addrequest from the MeNB 104 over the X2 interface, wherein the add requestcomprising of a plurality of SCells to the SeNB along with theassociated RRM measurements sent by the UE 108. Based on the receivedadd request, the SeNB 106 decides (602) a PSCell, wherein the PSCell canbe selected from the SCells received from the MeNB 104 based on the RRMmeasurements associated with the SCells and load information. Ondeciding the PSCell, the SeNB 106 sends (603) an add response to theMeNB 104, wherein the add response indicates the PSCell and the SCGconfiguration which includes at least the PSCell configuration i.e. theserving cell, configured with PUCCH resources for the UE, and optionallya plurality of SCells associated with SeNB 106. The MeNB 104 approvesthe received SCG configuration sent by the SeNB 106, and sends theresponse to SeNB. The SeNB 106 receives (604) an acknowledgement fromthe MeNB 104, wherein the acknowledgement comprises the security-basedkey for the UE 108 associated with SeNB 106. The MeNB 104 derives thesecurity base key of the UE 108 associated with the SeNB 106 based on atleast one of SCG counter and cell-specific parameters of the PSCell. TheSeNB 106 receives (605) the SN status count from the MeNB 104 and startsbuffering forwarded data sent by MeNB 104. The MeNB 104 sends the SCGconfiguration to the UE 108 and starts the path switch procedure towardsthe core network (CN) to offload the MCG bearer to the SeNB 106. The UE108 then performs the Random Access (RA) procedure on the cellconfigured with PUCCH resources for the UE 108 to get uplinksynchronized on at least the PSCell served on one of the frequenciesbelonging to the second set of frequencies associated with the SeNB 106.The SeNB 106 receives (606) the random access preamble from the UE 108and upon successful random access (RA) procedure; the SeNB 106establishes the L2 protocol stack and DRBs for data exchange with the UE108. With this procedure, the offloaded bearers are established on theSeNB 106 and the UE 108 starts operating in dual connectivity mode ofoperation with the MeNB 104 and SeNB 106. The MeNB 104 can receivemeasurement results from the UE 108 as the UE 108 continuously evaluatesthe measurement events, according to the measurement configurationreceived in the RRC reconfiguration message. The measurement resultscomprise of RRM measurement results for PCell associated with MeNB 104,PSCell associated with SeNB 106, other MCG and SCG SCells and so on. Onbasis of these measurement results, the MeNB 104 can further decide tochange or modify the SeNB configuration for the UE 108. The SeNB 106 canfurther receive (607) a modification message from the MeNB 104, whereinthe modification message can include either the RRM measurements sent bythe UE 108 associated with plurality of SCG SCells and/or new SCG SCelldecided to be added by the MeNB 104. Alternately the MeNB 104 canprovide to the SeNB 106 with a list of SCG cells in the modificationmessage meeting the PSCell measurement criterion. The SeNB 106determines (608) if a change in the PSCell is required based onmodification message received from MeNB 104. The process control thenmoves back to step 607 If SeNB 106 determines a change in the PSCell isnot required. If a change in the PSCell is required, the SeNB 106determines (609) the PSCell, wherein the PSCell can be determined basedon at least one of radio link quality and load information. The radiolink quality can be determined based on RRM measurements sent by the UE108 associated with plurality of SCG SCells and/or new SCG SCell decidedto be added by the MeNB 104 On determining the PSCell, the SeNB 106sends (609) an indication to the MeNB 104, wherein the indicationcomprises of the change in the PSCell and/or updated SCG configuration.The MeNB 104 generates an updated SeNB key, based on the new PSCelland/or updated SCG configuration. The SeNB 106 receives (611) theupdated SeNB key of the UE 108 from the MeNB 104. The various actions inmethod 600 can be performed in the order presented, in a different orderor simultaneously. Further, in some embodiments, some actions listed inFIGS. 6a and 6b can be omitted.

FIG. 7 illustrates the usage of the Events A2 and A4. These events (A2and A4) can be used only for addition/removal of the carrier, as shownin FIG. 7. A change of a serving cell is generally performed in order toavail the service from a better cell, which has better radiocharacteristics, resulting in the UE 108 utilizing a lower uplinktransmission power, or to a cell which has more resources for schedulingso that the data rate for the UE can be improved. Currently, a change ofa serving cell is governed using relative comparison of the currentlyserving cell and the measured neighbor cell.

Specifications have provisioned measurement events A3 and A5 forintra-frequency and inter-frequency measurement evaluation of a Pcellwith its neighbor cell. This is an indicating factor to the eNB/networkfor the existence of a better cell (stronger signal conditions) than thecurrently serving Pcell. The standards also provision a measurementevent A6 for evaluating best intra-frequency neighbors for Scell. Byusing A3 and A5, it can be ensured that the Pcell is the best cellavailable in that location and by using A6, it can be ensured that theScell is the best available component carrier on the provided frequency.

However, these events do not suffice the requirement to determinepScell/PSCell change to a better cell. Events A3 and A5 are presentlydefined only for change of Pcell and hence cannot be utilized for changeof pScell/PSCell. Event A6 cannot be extended for pScell change aspScell and Scell can be of different carrier frequencies and A6 catersonly to intra-frequency evaluations. If event A6 is extended tointer-frequency measurements, then it loses its purpose of finding thebest Scell on the configured component carrier.

Events A3 and A5 can be extended appropriately to meet the need forgoverning the change of the pScell. These events can be extended to dualusage (i.e., for neighbor comparison for both Pcell and pScell). A newdefinition needs to be defined for Event A3 and event A5. Followingextension is needed:

Event A3: A neighbor becomes offset better than PCell of UE associatedwith MeNB or Special cell (PSCell) of UE associated with SeNB.

Event A5: PCell of UE associated with MeNB 104 or Special Cell (PSCell)of UE associated with SeNB 106 becomes worse than threshold1 andneighbour becomes better than threshold2.

The above extension meets the following requirements:

Dual usage of Event A3/A5 i.e. for both PCell and pSCell.

Independent configuration of A3/A5 for PCell and pSCell

Independent triggering of A3/A5 for PCell and pSCell

Independent reporting of measurement results for Pcell and pSCell.

The UE 108 is aware which cell is its PCell (i.e. the cell on which itestablishes the RRC connection). The UE 108 is aware which cell is itspSCell (i.e. cell in SCG on which PUCCH resources are configured).

Independent configuration can be signaled in two ways (as depictedbelow).

Two possibilities to extend applicability of events A3/A5 to PCell orpSCell is provided: a modification to ReportConfigEUTRA or amodification to MeasObjectEUTRA.

Option 1: Modification to ReportConfigEUTRA

The network can choose to provide independent configuration for A3 andA5 evaluation for Pcell and pScell using an additional field in themeasurement configuration by modifying the field ReportConfigEUTRA asshown in FIG. 8b . Modification to ReportConfigEUTRA includes theaddition of a new Information element (IE) termed as cellGroup. This newIE can be configured with two distinct values (Pcell, pScell) indicatingthe UE about the cell group or eNodeB toward which the measurement isconfigured. For example, a reportConfigEUTRA configured for cellGroupPcell (for event A3) will indicate the UE that the correspondingmeasurement object (measurement id is linked to a measurement object anda reporting configuration) has to be evaluated for the change of Pcell(Neighbor becomes amount of offset better than PCell) and not for changeof pScell (Neighbour becomes amount of offset better than pSCell).

Had the network not configured this IE, then the UE would evaluate themeasurement object in comparison to both Pcell measurements as well aspScell measurements independently and send the measurement reports foreach of them when the reporting criterion is met.

Depicted below is an example wherein the ReportConfigEUTRA is modified,by addition of new fields as highlighted (in italics).

ReportConfigEUTRA information element ASN1START ReportConfigEUTRA ::=SEQUENCE { triggerType CHOICE { event SEQUENCE { eventId CHOICE {eventA1 SEQUENCE { a1-Threshold ThresholdEUTRA }, .....}, eventA3SEQUENCE { a3-Offset INTEGER (−30..30), reportOnLeave BOOLEAN cellGroupenum {Pcell, pSCell} }, .....}, eventA5 SEQUENCE { a5-Threshold1ThresholdEUTRA, a5-Threshold2 ThresholdEUTRA cellGroup enum{Pcell,pSCell} }, ..... ..., threshold-RSRQ RSRQ-Range } ASN1STOP

In an embodiment herein, the A3 and the A5 events are modified to beapplicable for a serving cell configured with the PUCCH resources forthe UE 108 on at most one second serving frequency served by the SeNB106 through reportConfigEUTRA.

Option 2: Modification to MeasObjectEUTRA

Network can choose to provide independent configuration for A3 and A5evaluation for Pcell and pScell using an additional field in themeasurement configuration by modifying the MeasObjectEUTRA in the RRCreconfiguration message as shown in FIG. 9b . Modification toMeasObjectEUTRA includes the addition of a new IE termed as cellGroup.This new IE can be configured with two distinct values (Pcell, pScell)indicating the UE 108 about the cell group or eNodeB toward which themeasurement is configured. For example, a MeasObjectEUTRA configured forcellGroup Pcell (for event A3) will indicate the UE 108 that thecorresponding measurement object (measurement id is linked to ameasurement object and a reporting configuration) has to be evaluatedfor the change of Pcell (Neighbour becomes amount of offset better thanPCell) and not for change of pScell (Neighbour becomes amount of offsetbetter than pSCell).

Had the MeNB 104 not configured this IE, then the UE would evaluate themeasurement object in comparison to both Pcell measurements as well aspScell measurements independently and used the measurement reports foreach of them when the reporting criterion is met.

Example for Modification to MeasObjectEUTRA by addition of new fields ashighlighted (in italics).

MeasObjectToAddModList information element --ASN1STARTMeasObjectToAddModList::= SEQUENCE(SIZ(1..maxObjectId))OFMeasObjectToAddMod MeasObjectToAddModList-v9e0::= SEQUENCE (SIZE(1..maxObjectId)) OF MeasObjectToAddMod-v9e0 MeasObjectToAddMod::=SEQUENCE { measObjectId MeasObjectId, cellGroupenum {Pcell, pSCell},measObject CHOICE { measObjectEUTRA MeasObjectEUTRA, measObjectUTRAMeasObjectUTRA, measObjectGERAN MeasObjectGERAN, measObjectCDMA2000MeasObjectCDMA2000, ... } } MeasObjectToAddMod-v9e0 :: =SEQUENCE {measObjectEUTRA-v9e0 MeasObjectEUTRA-v9e0 OPTIONAL-- Cond eutra }--ASN1STOP

In an embodiment herein, the A3 event and the A5 event are modified tobe applicable for a serving cell configured with the PUCCH resources forthe UE 108 on at most one second serving frequency served by the SeNB106 through measObject.

In an embodiment herein, where pScell change is governed by introducinga new event Ax, a new event is required for governing the change ofpScell where a relative comparison can be performed between the servingpScell and a neighbour cell belonging to a different frequency but thesame eNodeB. The evaluation is performed as per the below expressionensuring that the neighbor cell is an offset better than the pScell. Theentering and leaving condition for this event is defined below:Event Ax=>(Ncell−hysteresis)>(pScell+offset)  Entering condition:Event Ax=>(Ncell+hysteresis)<(pScell+offset)  Leaving condition:

Ncell and pScell represent the measurement values for neighbor cell andpScell and offset represents the measurement offset configured by thenetwork.

The Ax event is an event defined for a serving cell configured with thePUCCH resources for the UE 108 on at most one second serving frequencyserved by the SeNB 106.

In an embodiment herein, wherein a new field in the measurement reportmessage is introduced, the network should be able to distinguishmeasurement results for PCell and pSCell, which requires the followingchanges:

Modification to MeasResults

Need to add new IE as highlighted below

Modification to MeasResults includes the addition of a new IE termed asmeasResultpSCell. This new IE can be configured with two distinctvariables (rsrpResult, rsrqResult) indicating the eNodeB about themeasurement values of the serving pScell once it has satisfied theconfigured reporting criteria. The current standard specification (3GPPTS 36.331) does not have the provision to report the measurements forpScell and a new IE has to be provisioned.

MeasResults information element --ASN1START MeasResults ::=SEQUENCE {measId MeasId, measResultpSCell SEQUENCE { rsrpResult RSRP-Range,rsrqResult RSRQ-Range }, csg-Identity-r9 CSG-Identity OPTIONAL }--ASN1ST0P

FIGS. 11a, 11b and 11c illustrate methods for linking of measurementevents based on absolute thresholds and example scenarios when the TTTis expired for only one configured measurement event but reporting isdone for linked measurement events associated with correspondingmeasurement IDs, according to embodiments as disclosed herein.

The indication for linking of measurement identities is configuredthrough the reportConfigEUTRA and is used to link measurement eventassociated with measurement object belonging to one configured frequencyto the measurement event associated with another measurement objectbelonging to another configured frequency.

Measurement event A1 is configured to be reported when the configuredserving cell is determined to be above a configured threshold value.This event can also serve as a trigger to the network for deactivatingcertain measurements.

Measurement event A2 is configured to be reported when the configuredserving cell is determined to be below a configured threshold value.This event also serves as a trigger to activate new measurements also toremove CCs/Scell (Scell removal).

Measurement event A4 is configured to be reported when a neighbor cellon a configured frequency is determined to be above a configuredthreshold value. This event also serves as a trigger to add new CCs as Scell (Scell addition).

Therefore, using a combination of event A2 and A4 and setting the rightthresholds for each of them, it can be indicated to the network that aneighbor cell is better than the serving cell by an offset as indicatedin FIG. 11a . This is the same information that event A3, A5 or A6 wouldgive to the network depending on its configuration. However, 2measurement events cannot be triggered and reported at the sameinstantaneous time to the network. Network can take action on thereception of 1 event even before the next event is reported and thedesired outcome cannot be achieved. As an example, if A2 and A4 areconfigured at the same time and A2 is met first and reported while theevent A4 is still being evaluated, network on receiving A2 can choose toremove the Scell for which A2 is reported. Similarly, if event A4 isreported while A2 is getting evaluated, network can choose to add asecondary component carrier before receiving A4 report. Therefore, thedesired actions of replacing the serving cell with the evaluatedneighbor cell cannot be achieved optimally. In order to avoid thisundesired behavior, embodiments herein disclose a mechanism of linkingthe two measurement events.

Method 1: Indication for Linking of Measurements.

The Linking of measurements has to be indicated by the Network inmeasurement configuration. It can add as either new IE which willindicate what all meas id can be linked to each other. IE can be definedas “Link info” or measid_Link. In this IE multiple meas id can bementioned which can be linked to each other. While sending the report tothe Network, UE can send the value of meas id for event for whichcondition has been satisfied. This can help the NW to take appropriatedecision.

The decision for linking of measurements can either be network signaled(by the MeNB 104) or UE 108 triggered. If the network signals thelinking, then the Information Element (IE) measid_Link is signaled inthe measurement configuration with the list of measurement ids that canbe linked together and sent in a single measurement report. The methodand sequence of procedures involved at the UE 108 for performing thistype of linked measurement reporting is illustrated in the flow chart inFIG. 12. If the linking is initiated due to UE 108 trigger conditions,then the information element LinkedMeasPresent has to be included andset to TRUE while sending the measurement report for the measurement id,which has successfully satisfied the reporting configuration. The methodand sequence of procedures involved at the UE for performing this typeof linked measurement reporting is illustrated in the flow chart in FIG.12. The below mention methods are applicable to UE as well as NWinitiated linking.

Method 2: Linking of Measurement Events Based on Absolute NeighborMeasurement

In this method, both the measurement events as indicated by the network104 are linked and reported together, if one of the measurement eventsmeets the criteria. The report is sent irrespective of whether thesecond cell has met the entry criteria for the event. Consider the NW104 has configured Event A2 and event A4 and send the measurementconfiguration by linking both of these events for particular object. Inthis method, measurements of 2 measurement ids are linked if one of themeasurement id reporting criteria is satisfied (irrespective of thecondition of the other measurement id if it is already detected).

Case 1: When TTT Running for Both Measurement Ids (as Described Below inFIG. 12)

FIG. 12 is a flowchart explaining sequence of procedures involved at theUE when measurement linking between multiple measurement ids or eventsis signaled/initiated, according to embodiments as disclosed herein.Initially, a RRC connection is established (1201) between the UE 108 andthe MeNB 104 Further, the MeNB 104 sends (1202) a RRC reconfigurationmessage with measurement configuration to the UE 108. After sending theRRC reconfiguration message, a Meas ID 1 for object 1 and A2 event isconfigured (1203). Similarly, a Meas ID 2 is configured (1203) forobject 1 and A4 event. The UE 108 further evaluates (1204) serving celland a neighbour cell to identify occurrence of at least one of event A2or event A4. If event A2 is detected (1205), then the UE 108 checks(1206) to identify presence of measid_link in the measurementconfiguration. If the measid_link is detected in the measurementconfiguration, then the UE 108 sends (1207) measurement report for themeasurement ID 1, links (1207) the measurement ID 2 measurements in thereport and stops (1207) evaluation of measurement id 2. If an additionalside condition for linking is met, the UE 108 sets the IELinkedMeasePresent field to TRUE. If the measid_link is not detected inthe measurement configuration, then the UE 108 sends (1208) measurementreport for measurement id 1.

If event A4 is detected, then the UE 108 checks (1209) if measid_link ispresent in the measurement configuration. If the measid_link isdetected, then the UE 108 sends (1210) measurement report formeasurement id 2, links (1210) the measurement ID 1 measurements in thereport and stops (1210) evaluation of measurement id 1. If an additionalside condition for linking is met, the UE 108 sets the IELinkedMeasePresent field to TRUE. If the measid_link is not detected inthe measurement configuration, then the UE 108 sends (1212) measurementreport for measurement id 2.

The various actions in method 1500 can be performed in the orderpresented, in a different order or simultaneously. Further, in someembodiments, some actions listed in FIG. 12 can be omitted.

FIG. 13 illustrates an example scenario of network decisions whenmeasurement report is sent to network after satisfying the criteria forevent A1, A2 or A4, according to embodiments as disclosed herein.

The UE 108 receives a measurement configuration for event A1, A2, and/orA4 from the MeNB 104. Upon receiving the measurement configuration, theUE 108 evaluates a serving cell for occurrence of at least one of theevents A1, A2, and/or A4. Further, for the event detected, the UE 108prepares a measurement report and transmits the report to the MeNB 104.By analyzing contents of the report received, the MeNB 104 identifiesthat event that has been detected in the UE 108.

If the event detected is A1, the MeNB 104 releases event A2,reconfigures events A4 and A6. If the event detected is A2, the MeNB 104releases event A1, reconfigures event A2 and one of events A4 and A6.The MeNB 104 further releases the SCell. If the event detected is A4,the MeNB 104 reconfigures one of event A1 or event A2, one of event A4or event A6, and event A3. The MeNB 104 further configures SCell andreleases other SCells. Further, based on the changes made, the MeNB 104sends a measurement reconfiguration to the UE 108, which is based on thereported event.

FIG. 14 illustrates an example scenario of network decisions whenmeasurement report is sent to network after meeting the leaving criteriafor event A2 or A4, according to embodiments as disclosed herein.

The UE 108 receives a measurement configuration message for one ofA1/A2/A4 from the MeNB 104 (which can be at least one of the MeNB 104 orthe SeNB 106. Upon receiving the measurement configuration, the UE 108evaluates a serving cell for occurrence of at least one of the eventsA1, A2, and A4. Further, for the event detected, the UE 108 prepares ameasurement report, and transmits the report to the MeNB 104. Byanalyzing contents of the report received, the eNB identifies that eventthat has been detected in the UE 108.

If the event detected is A1, the MeNB 104 releases A2, reconfigures A4and A6. If the event detected is A2, the MeNB 104 releases A1,reconfigures A2 and one of A4 and A6. The eNB further releases theSCell. If the event detected is A4, the MeNB 104 reconfigures one of A1and A2, one of A4 and A6, and A3. The MeNB 104 further configures SCell,and releases other SCell.

The MeNB 104 further receives from the UE 108 a measurement report (MR),which indicates that the UE 108 is leaving at least one of the eventsA1/A2/A4. If the MR indicates that the UE 108 intends to leave event A1,the MeNB 104 reconfigures A1, A2, and one of A4 and A6. If the MRindicates that the UE 108 intends to leave event A2, the MeNB 104reconfigures A1, A2, and one of A4 and A6. The MeNB 104 decides tocontinue SCell. If the MR indicates that the UE 108 intends to leaveevent A4, the MeNB 104 reconfigures A1, A2, and one of A4 and A6.Further, based on the change of settings decided, the MeNB 104 sends ameasurement reconfiguration message to the UE 108.

FIG. 15 is a block diagram illustrating various modules of a MeNB 104and a SeNB 106, according to embodiments as disclosed herein. Theprimary blocks present for communication to enable dual connectivitymode in a UE 108 include a communication module 1502, acontrol-signaling module 1504, a processor module 1506, a memory module1508 and a radio resource management module 1510. In an embodiment, thecommunication module 1502 is configured to communicate PSCellinformation to the UE 108 and other eNB for establishing the SCG. Forexample, the wireless communication module 1502 in a MeNB 104 can beconfigured to communicate the SeNB configuration and PSCell informationto one or more UEs 108.

The control-signaling module 1504 determines the radio resource control(RRC) messages to be transmitted over the air interface to the UE. Thecontrol-signaling module 1504 also determines the X2-AP messages to betransmitted by the MeNB 104 to SeNB 106 or from the SeNB 106 to MeNB 104over the X2 interface 110. The type of RRC messages used is based onseveral configurations provided for the UE 108, which include forexample, but are not limited to, RRC connection reconfiguration message,typically used to provide measurement configuration and handover commandto the UE. The types of X2-AP messages used is again based on severalprocedures executed between the MeNB 104 and SeNB 106, which includesfor example, but are not limited to, X2 message for adding one or moreSCells in the SeNB.

Further, the memory module 1508 is configured to store data related tooperation of the eNB's (MeNB and SeNB) and the UE 108. The memory module1508 can be configured to store various UE capabilities andconfigurations provided to the UE.

The radio resource management module 1510 is mainly responsible for datascheduling to the UE 108. The radio resource management module 1510 isfurther configured to handle the addition and removal of plurality ofSCells handled by the MeNB or SeNB. The MeNB 104 and SeNB 106 canconfigure the radio resource management module 1510 to generatetransport blocks from the various DRBs handled.

FIG. 16 is a block diagram illustrating various modules of a UE,according to embodiments as disclosed herein. The primary blocks toenable dual connectivity mode in the UE 108 include a communicationmodule 1602, a control-signaling module 1604, a processor module 1606, amemory module 1608 and a radio resource management module 1610.

In an embodiment, the communication module 1602 is configured to receivePSCell information. For example, the wireless communication module 1602in a UE 108 can be configured to communicate the SeNB configuration andPSCell information from the MeNB 104.

The control-signaling module 1604 determines the radio resource control(RRC) messages to be transmitted over the air interface to/from the UE.The control-signaling module 1504 also determines the configurationsprovided for the UE 108, which include for example, but are not limitedto, RRC connection reconfiguration message, typically used to providemeasurement configuration and handover command to the UE.

Further, the memory module 1608 is configured to store data related tooperation of the UE 108. The memory module 1608 can be configured tostore various UE capabilities and configurations provided to the UE 108.

The radio resource management module 1610 is mainly responsible for datascheduling from the UE 108. The MeNB 104 and SeNB 106 can configure theradio resource management module 1610 to generate transport blocks fromthe various DRBs handled.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the embodiments herein that others can, byapplying current knowledge, readily modify and/or adapt for variousapplications such specific embodiments without departing from thegeneric concept, and, therefore, such adaptations and modificationsshould and are intended to be comprehended within the meaning and rangeof equivalents of the disclosed embodiments. It is to be understood thatthe phraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodimentsherein have been described in terms of preferred embodiments, thoseskilled in the art will recognize that the embodiments herein can bepracticed with modification within the spirit and scope of theembodiments as described herein.

What is claimed is:
 1. A method performed by a master base station in awireless communication system where a terminal is capable ofcommunicating with the master base station and a secondary base station,the method comprising: transmitting, to a terminal, a control messageincluding a first measurement configuration of at least one of an A3event or an A5 event for a primary cell for a master base station and asecond measurement configuration of at least one of an A3 event or an A5event for a primary cell for a secondary base station; receiving, fromthe terminal, a measurement report determined based on the controlmessage; transmitting, to the secondary base station, a request messageincluding a measurement result for one or more cells based on themeasurement report; and receiving, from the secondary base station, aresponse message including configuration information for change of aprimary cell for the secondary base station as a response to the requestmessage.
 2. The method of claim 1, further comprising: transmitting, tothe terminal, a message for a connection configuration, the message forthe connection configuration including the configuration information forchange of the primary cell for the secondary base station; andreceiving, from the terminal, a response message in response to themessage for the connection configuration.
 3. The method of claim 1,wherein the primary cell for the secondary base station is configuredwith physical uplink control channel (PUCCH) resources.
 4. The method ofclaim 1, wherein the A3 event corresponds to an event in which ameasurement result for a neighboring cell of the terminal is offsetbetter than a measurement result for a primary cell, and the A5 eventcorresponds to an event in which a measurement result for a primary cellis smaller than a first threshold and a measurement result for aneighboring cell of the terminal is better than a second threshold.
 5. Amethod performed by a secondary base station in a wireless communicationsystem where a terminal is capable of communicating with a master basestation and the secondary base station, the method comprising:receiving, from a master base station, a request message including ameasurement result for one or more cells, wherein the measurement resultis determined based on a measurement report, wherein the measurementreport is determined based on a control message, and wherein the controlmessage includes a first measurement configuration of at least one of anA3 event or an A5 event for a primary cell for the master base stationand a second measurement configuration of at least one of an A3 event oran A5 event for a primary cell for a secondary base station; determininga primary cell for the secondary base station among the one or morecells based on the request message; transmitting, to the master basestation, a response message including configuration information forchange of a primary cell for the secondary base station as a response tothe request message; performing a process for a random access towardsthe determined primary cell for the secondary base station with aterminal; receiving, from the master base station, information ofsequence number (SN) status; and receiving data forwarded from themaster base station.
 6. The method of claim 5, wherein the primary cellfor the secondary base station is configured with physical uplinkcontrol channel (PUCCH) resources.
 7. A method performed by a terminalin a wireless communication system where the terminal is capable ofcommunicating with a master base station and a secondary base station,the method comprising: receiving, from a master base station, a controlmessage including a first measurement configuration of at least one ofan A3 event or an A5 event for a primary cell for the master basestation and a second measurement configuration of at least one of an A3event or an A5 event for a primary cell for a secondary base station;transmitting, to the master base station, a measurement report based onthe control message; receiving, from the master base station, a messagefor a connection configuration, the message for the connectionconfiguration including configuration information of a primary cell forthe secondary base station; transmitting, to the master base station, aresponse message in response to the message for the connectionconfiguration; and performing a process for a random access to thesecondary base station based on the configuration information of theprimary cell for the secondary base station.
 8. The method of claim 7,wherein the primary cell for the secondary base station is configuredwith physical uplink control channel (PUCCH) resources.
 9. The method ofclaim 7, wherein the A3 event corresponds to an event in which ameasurement result for a neighboring cell of the terminal is offsetbetter than a measurement result for a primary cell, and the A5 eventcorresponds to an event in which a measurement result for a primary cellis smaller than a first threshold and a measurement result for aneighboring cell of the terminal is better than a second threshold. 10.A master base station in a wireless communication system where aterminal is capable of communicating with the master base station and asecondary base station, the master base station comprising: atransceiver; and at least one processor configured to: transmit via thetransceiver, to a terminal, a control message including a firstmeasurement configuration of at least one of an A3 event or an A5 eventfor a primary cell for a master base station and a second measurementconfiguration of at least one of an A3 event or an A5 event for aprimary cell for a secondary base station, receive via the transceiver,from the terminal, a measurement report determined based on the controlmessage, transmit via the transceiver, to the secondary base station, arequest message including a measurement result for one or more cellsbased on the measurement report, and receive via the transceiver, fromthe secondary base station, a response message including configurationinformation for change of a primary cell for the secondary base stationas a response to the request message.
 11. The master base station ofclaim 10, wherein the at least one processor is further configured to:transmit via the transceiver, to the terminal, a message for aconnection configuration, the message for the connection configurationincluding the configuration information for change of the primary cellfor the secondary base station, and receive via the transceiver, fromthe terminal, a response message in response to the message for theconnection configuration.
 12. The master base station of claim 10,wherein the primary cell for the secondary base station is configuredwith physical uplink control channel (PUCCH) resources.
 13. The masterbase station of claim 10, wherein the A3 event corresponds to an eventin which a measurement result for a neighboring cell of the terminal isoffset better than a measurement result for a primary cell, and the A5event corresponds to an event in which a measurement result for aprimary cell is smaller than a first threshold and a measurement resultfor a neighboring cell of the terminal is better than a secondthreshold.
 14. A secondary base station in a wireless communicationsystem where a terminal is capable of communicating with a master basestation and the secondary base station, the secondary base stationcomprising: a transceiver; and at least one processor configured to:receive via the transceiver, from a master base station, a requestmessage including a measurement result for one or more cells, whereinthe measurement result is determined based on a measurement report,wherein the measurement report is determined based on a control message,and wherein the control message includes a first measurementconfiguration of at least one of an A3 event or an A5 event for aprimary cell for the master base station and a second measurementconfiguration of at least one of an A3 event or an A5 event for aprimary cell for a secondary base station, determine a primary cell forthe secondary base station among the one or more cells based on therequest message, transmit via the transceiver, to the master basestation, a response message including configuration information forchange of a primary cell for the secondary base station as a response tothe request message, perform a process for a random access towards thedetermined primary cell for the secondary base station with a terminal,receive via the transceiver, from the master base station, informationof sequence number (SN) status, and receive via the transceiver, dataforwarded from the master base station.
 15. The secondary base stationof claim 14, wherein the primary cell for the secondary base station isconfigured with physical uplink control channel (PUCCH) resources.
 16. Aterminal in a wireless communication system where the terminal iscapable of communicating with a master base station and a secondary basestation, the terminal comprising: a transceiver; and at least oneprocessor configured to: receive via the transceiver, from a master basestation, a control message including a first measurement configurationof at least one of an A3 event or an A5 event for a primary cell for themaster base station and a second measurement configuration of at leastone of an A3 event or an A5 event for a primary cell for a secondarybase station, transmit via the transceiver, to the master base station,a measurement report based on the control message, receive via thetransceiver, from the master base station, a message for a connectionconfiguration, the message for the connection configuration includingconfiguration information for change of a primary cell for the secondarybase station, transmit via the transceiver, to the master base station,a response message in response to the message for the connectionconfiguration, and perform a process for a random access to thesecondary base station based on the configuration information of theprimary cell for the secondary base station.
 17. The terminal of claim16, wherein the primary cell for the secondary base station isconfigured with physical uplink control channel (PUCCH) resources. 18.The terminal of claim 16, wherein the A3 event corresponds to an eventin which a measurement result for a neighboring cell of the terminal isoffset better than a measurement result for a primary cell, and the A5event corresponds to an event in which a measurement result for aprimary cell is smaller than a first threshold and a measurement resultfor a neighboring cell of the terminal is better than a secondthreshold.